1. Field of the Invention
The present invention relates to an apparatus and method of analyzing a magnetic random access memory (MRAM). More particularly, the present invention relates to an apparatus and method of analyzing an MRAM, which is capable of quickly analyzing all characteristics of the MRAM.
2. Description of the Related Art
Magnetic Random Access Memory (MRAM), a type of nonvolatile memory, is a solid-state magnetic memory that uses a magnetoresistance effect based on a nano magnetic material's characteristic effect of spin dependent tunneling. The MRAM uses a giant magnetoresistance (GMR) effect or a tunnel magnetoresistance (TMR) effect that occurs because spin of an electron (i.e., degree of freedom of an electron) greatly influences electron transfer. A conventional MRAM includes a cell array, in which word lines extend along rows of memory cells and bit lines extend along columns of memory cells. More specifically, memory cells are located at intersections of word lines and bit lines. Each memory cell includes two magnetic layers, i.e., a fixed layer and a free layer. The fixed layer is magnetically fixed and the free layer has a variable magnetization direction. The memory cell stores a data bit according to a relative magnetization orientation of the fixed layer and the free layer.
There is a limitation on selection of a material for a memory because low power consumption is required to commercialize the memory. A conventional MRAM uses permalloy (NiFe) in a switching field, that is, the free layer of the magnetoresistance element, in order to reduce power consumption. Increase of magnetoresistance is essential to increase an operating speed of an MRAM and for efficient design of chip architecture. To achieve this increase of magnetoresistance, a magnetic thin layer used in the free layer must have a ferromagnetic characteristic and a high polarization characteristic.
An MRAM having the above structure, for example, a tunnel magnetoresistance (TMR) structure, distinguishes data “0” and “1” by measuring a variation of tunnel resistances according to magnetic states of the two ferromagnetic layers, which are separated by a tunnel barrier. There are various non-uniform states during switching of the magnetic states of the ferromagnetic layers (free layers), i.e. writing data on the memory. Non-uniform states cause erroneous operation of the memory.
Generally, there are two factors that cause non-uniform switching states of the memory. FIGS. 1A and 1B are graphs and illustrations in connection with non-uniform switching states. FIG. 1A includes a graph plotting magnetic characteristics of spins of the free layer within a domain against an applied magnetic field when the spins are arrayed in a vortex structure, as shown in the illustration below the graph in FIG. 1A. In this structure, the free layer is made of a ferromagnetic material and provided in the MRAM structure. FIG. 1B is a graph plotting magnetic characteristics of spins of the free layer within a domain when the spins are in a fixed state at some portion, as shown in the illustration below the graph in FIG. 1B. In such a structure, the MRAM exhibits non-uniform switching states.
To determine non-uniform switching states of an MRAM, a measurement device that systematically measures characteristics of the MRAM is necessary. A conventional method of measuring switching characteristics of the MRAM is accomplished by measuring resistance of a unit cell under a magnetic field in every unit cell. In this case, a significant amount of time is required to measure all properties of an MRAM array at a wafer level because it takes time for the magnetic field to be stabilized. Conventionally, a method of synchronizing a resistance measurement with the magnetic field has been introduced in an effort to increase measurement speed. However, this conventional method cannot measure remanence, and, thus, the cause of the non-uniform switching process in the MRAM cannot be identified.